In prior U.S. Pat. Nos. 4,945,687 and 5,046,288, there is disclosed a rotary finishing tool where monofilaments such as extruded nylon containing abrasive grains are used as reinforcement in a relatively heavy foam elastomer which contains at least one grit size type of abrasive and preferably two grit size types, one of which is relatively coarse. The foam elastomer bond has a void content of from about 5 to about 50 percent. Tools made according to such patents typically have elastomeric densities of from 20 to 50 pounds per cubic foot and higher. The inclusion of the nylon abrasive monofilaments allows the tool to be run at higher speeds. The tools of such prior patents have the characteristics of improved soft grinding wheels with the abrasive being delivered to the work primarily through the elastomer. While effective as a high speed material removal tool, such tools are not effective for surface finish and edge blending operations where the tool would run at a slower or more normal speed such as 2000 to 2500 feet per minute, and at considerably higher pressure.
Lateral distortion of an abrasive monofilament is to be expected at high working pressures. Such lateral distortion is where the tip of the monofilament is deflected to one side or the other of the plane of rotation as it engages the work. This produces a non-linear scratch pattern and reduces the efficiency of the tool. In primary metal finishing, where metal is made in bulk, usually in strip form, a straight line or generally linear scratch pattern is very important. Before subsequent operations, the strip, usually coiled, is uncoiled and run through surface finishing tool stands where both surfaces are subjected to the normal speed high pressure surface finishing operation. The strip may be quite wide and the tools span the width of the strip. The tools are usually run with coolant. In some cases, the coolant is introduced at the working face and in others, the coolant is introduced at the axis or arbor of the tool to flow radially outwardly to the working face. The coolant removes loose abrasive particles, anything worn from the tool, and anything removed from the metal. The coolant is run through a filter which takes out some of the particles, but not all. Some, mostly detritus, remains entrained in the coolant and over time, tends to clog up between the tool sections. This is particularly true if the coolant moves through the core of the tool to pass radially. This is the most effective cooling system for an abrasive nylon monofilament tool since it keeps the whole length of the monofilament at the proper temperature.
If the proper coolant flow is blocked, the plastic of the monofilament may become soft or melt and this may very quickly ruin a very expensive tool. For a wide strip, such tools may cost many thousands of dollars. Also, and perhaps more importantly, if the tool clogs, the line has to be shut down, the tool disassembled, and if the foreign material has dried, it literally has to be sand blasted to clean the tool properly.
High application pressure with plastic abrasive monofilaments rather highly compacted and with a high abrasive loading will normally generate more heat than normal. Also, high pressure tends to compact the monofilaments, and if the interstices are relied on for coolant flow, such compression tends to close any normal separation or voids. If detritus is in the coolant system and not removed by upstream filters, the tool will clog and may soon self destruct because of lack of coolant flow. While the exterior of the tool may in some cases be sand blasted to remove clogging particles, the interior interstices cannot. The clogging and heat rise may happen suddenly resulting in the destruction of the tool.
Where a high density matrix is employed, particularly one which incorporates abrasive of some coarseness, tool wear tends to form rather sizable clumps, or particles. In some applications, this is not a particular problem. However, in primary metal finishing or edge blending where high pressures are employed continuous recirculated coolant is required and such high density material creates particles which can quickly clog filters or coolant flow paths which can quickly lead to expensive consequences. High density materials which have a liquid state upon erosion also tend to agglomerate other particles to form clumps, particularly when abrasive or coarse abrasive is used. Accordingly, it would be desirable to have a matrix which does not create clogging clumps as it wears away. It would also be desirable that under normal wear or erosion that the matrix material go from a solid to primarily gas, and that what particles are produced, do not create problems, due to particle size, velocity and weight or mass.
It would, accordingly, be desirable to have a low cost highly efficient surface finishing and edge blending tool which would produce a straight or generally linear scratch pattern and not be subject to clogging or coolant filter problems.
While abrasive plastic monofilaments both circular and rectangular in section have been used in a variety of tools, such monofilaments are limited in the amount of abrasive which may be entrained during extrusion. The tough plastic material provides the tensile and modular strength, and at high abrasive loading particularly with large grit size abrasive, the strength of the abrasive monofilament declines. This is particularly true in high pressure surface finishing or edge blending operations where lateral distortion or flexing is apt to occur. With high abrasive loading, abrasive monofilament breakage, fracture, and premature wear is to be expected at high working pressures. It would also be desirable to have such a tool capable of operating at such high pressures and yet have a high abrasive loading of the monofilaments, both in amount and grit size.